3.3. Effects of strain and temperat

3.3. Effects of strain and temperature on the efficiency of power dissipationFig.10 (a) shows the variation of efficiency of power dissipation ( ) of the alloy with temperature at true strain of 0.7. The value of exhibit different variation tendencies at different strain rate with the increasing of temperature. At strain rate of 0.01s-1 and 0.1s-1, the value is about 0.4 and slightly decreases with the temperature increase, which suggest that the temperature has no significant effect on the workability of the alloy. But as the strain rate decreased to 0.001 s-1, except that there is a slight decrease under deformation temperature of 400℃, the value exhibits no change. At 1s-1 high strain rate condition, the value increase rapidly with the increase of temperature, and then display stable state. Fig.10(b) shows the effects of strain on the value of the test alloy at strain rate of 0.01s-1. At temperature of 350℃, the value increases drastically from the minimum to the maximum, and then decrease to about 0.45, the maximum value of 0.5 is obtained at strain of 0.7. With temperature increased to 400℃, the variation tendency of the value is consistent with 350℃. At high temperature of 450℃ and 500℃, the value of decrease gradually with the increase of strain.The efficiency of power dissipation, which is a dimensionless parameter, can be used to reflect the microstructure evolution of the alloy during deformation. At high strain rate (1s-1), the negative and relative lower value indicated the unstable microstructure evolution of the alloy during deformation, which is related to the dynamic strain aging and the initiation and growth of microcracks [26-27]. At 0.1s-1 and 0.01s-1 intermediate strain rate, gentle variation of value with the increase of temperature manifested the stable microstructure evolution of the alloy during deformation.